Epic: Navigation & home-screen redesign — bottom tab bar (Prop A)

[burkben]

Background

v1.0 shipped with the home screen as a hub: the speedometer plus a vertical stack of six full-width buttons (Race, Garage, History, Achievements, Settings, Live log). It works, but it doesn't scale, it requires scrolling, and every mode switch means routing back through Home.

This epic realigns navigation to the pattern already described in docs/architecture/ui-and-design.md §2 (bottom tabs) — "Proposal A" from our design exploration: a persistent bottom tab bar for the primary modes, with a "More" sheet for the rest.

It also sets up two adjacent improvements:

• The home screen becomes a proper hero (live speedometer + a model of the last-scanned car).
• The connection UX is modernized: the app auto-connects, and the status pill becomes the connect/disconnect control (the dedicated "Connect portal" button goes away).

Design language

Captured in docs/architecture/design-language.md (added as part of this initiative) — colors, type, spacing, the navigation model, core components, motion/haptics, and the connection-UX principle.

Stories

• Adopt bottom-tab navigation (Speed · Race · Garage · History · More) #29 — Adopt bottom-tab navigation (Speed · Race · Garage · History · More)
• Add a "More" overflow sheet (Achievements · Live portal · Settings) #30 — Add a "More" overflow sheet (Achievements · Live portal · Settings)
• Show a last-scanned car hero on the Speedometer screen #31 — Show a last-scanned car hero on the Speedometer screen
• Auto-connect to the portal on launch (no Connect button) #32 — Auto-connect to the portal on launch (no Connect button)
• Make the status pill the connect/disconnect control; remove "Connect portal" button #33 — Make the status pill the connect/disconnect control; remove "Connect portal" button

Out of scope / future

• Full 3D car rendering (start with art/identity; model is a follow-up).
• First-run pairing / onboarding screen.
• Sound design.

Note

A short ADR may be warranted for the Stack → Tabs navigation decision and the auto-connect default — see the ADR process in docs/adr/.